Dehydrogenation of n-butane to butenes

ABSTRACT

A catalyst composition suitable for the conversion of n-butane to butenes. The same catalyst composition that with chlorination is further suitable, when used in the conversion of n-butane, for the production of an increased amount of BTX (benzene-toluene-xylene) and greater selectivity to the production of isobutylenes than attained with the unchlorinated catalyst. A process for the preparation of catalyst compositions suitable for the conversion of n-butane. Use of the catalyst compositions in processes for the conversion of n-butane.

This application is a Division of application Ser. No. 09/222,470, filedDec. 29, 1998 now U.S. Pat. No. 6,133,192.

FIELD OF THE INVENTION

The invention relates to a catalyst suitable for the dehydrogenation ofn-butane to butenes that with chlorination is further suitable, whenused in the conversion of n-butane, for the production of an increasedamount of BTX (benzene-toluene-xylene) and greater selectivity to theproduction of isobutylenes than attained with the unchlorinatedcatalyst; a process for the preparation of catalyst suitable for theconversion of n-butane and the use of the catalyst in processes for theconversion of n-butane.

BACKGROUND OF THE INVENTION

It is known that n-butane can be converted to other hydrocarbons in thepresence of variety of catalyst supports impregnated with a variety ofmetals. A catalyst composition prepared according to a process of thisinvention has been found to be suitable for use in the dehydrogenationof n-butane to butenes. It has also been found that upon chlorination ofthis catalyst its suitability for use in the production of BTX fromn-butane is improved.

SUMMARY OF THE INVENTION

It is an object of this invention to at least partially dehydrogenaten-butane to butenes.

Another object of this invention is to provide an improved alumina-basedcatalyst that can be utilized in the dehydrogenation of n-butane tobutenes.

A further object of this invention is to provide a method for making analumina-based catalyst that can be utilized in the dehydrogenation ofn-butane to butenes.

It is another object of this invention to provide a chlorinatedalumina-based catalyst.

Another object of the invention is to utilize a chlorinatedalumina-based catalyst in the production of BTX from n-butane.

Still another object of the invention is to provide a method forpreparing a chlorinated alumina-based catalyst that can be utilized inthe production of BTX from n-butane.

The invention is an alumina-based catalyst that is prepared byimpregnation with tin, steam treatment, impregnation with platinum andcalcination in air to provide a catalyst composition and a process inwhich a feedstock containing n-butane is passed in contact with thiscatalyst composition under conditions to produce butenes. The inventionalso includes a catalyst composition prepared by the chlorination of thecatalyst produced as set out above and a process in which a feedstockcontaining n-butane is passed in contact with this catalyst compositionunder conditions to produce BTX.

Other objects and advantages of the invention will become apparent fromthe detailed description and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The alumina used in making the inventive compositions can be any aluminawhich when contacted with a feedstock containing n-butane under suitableoperating conditions is not detrimental to the conversion of n-butane tobutenes. The alumina can be alpha-alumina, beta-alumina, gamma-alumina,eta-alumina, delta-alumina, or combinations of any two or more thereof.The presently preferred alumina is gamma-alumina having a surface areain the range of about 40 m²/g to about 300 m²/g, a total pore volume inthe range of about 0.1 ml/g to about 1 ml/g. These aluminas arecommercially available as extrudate pellets.

According to the present invention any tin-containing compound whichwhen combined with alumina is effective in producing butenes from theconversion of n-butane can be employed. Examples of preferred compoundsare organic tin compounds that can be dissolved in organic solvents,these include, but are not limited to, tributyl tin acetate,trimethyltin, tetra-n-propyltin, tributyl tin hydride, trimethyl tinhydroxide, tri-n-propyltin hydroxide, tri-n-propyltin acetate, andmixtures of two or more thereof. Tributyl tin acetate is most preferred.

The amount of tin incorporated or impregnated into the alumina shouldprovide a concentration effective to assure predetermined buteneconversion yields employing the catalyst composition in the selectivedehydrogenation of feedstock that contains n-butane. Generally, theweight percent of tin present in the impregnated alumina is in a rangeof about 0.001 to about 10 weight percent of the impregnated aluminacomposition. The preferred concentration of tin in the impregnatedzeolite is in the range of about 0.01 to about 5 weight percent and,more preferably, from about 0.1 to about 2 weight percent of theimpregnated zeolite composition.

It is essential to this invention that the alumina impregnated with tinbe treated in the presence of steam at an elevated temperature. In thepreferred embodiment of the invention the alumina impregnated with tinis a tin-aluminate.

Generally, this steam treatment can be conducted at a pressure in arange from below atmospheric pressure to about 1000 pounds per squareinch absolute (psia). More typically, however, the pressure range isfrom about atmospheric to about 100 psia. The temperature of this steamtreatment is generally in the range of about 400° C. to about 1000° C.Preferably, this temperature range is from about 500° C. to about 850°C. and, most preferably, the temperature of this heat treatment is in arange of about 550° C. to about 750° C.

The steam treated tin-aluminate is then impregnated with a platinumcompound. Generally, any platinum-containing compound can be employed inthe process of this invention. Examples of suitable platinum compoundsinclude, but are not limited to, chloroplatinic acid, platinic chloride,platinum bromide, platinum iodide, tetramine platinum chloride,tetramine platinum nitrate, tetramine platinum hydroxide,tetrachlorodiamine platinum and combinations of any two or more thereof.Chloroplatinic acid is preferred.

The impregnating solution is an aqueous solution to which can be added asmall amount of acid to aid in stabilizing the impregnating solution.Presently, when chloroplatinic acid, the preferred platinum compound, isused, hydrochloric acid (HCl) is added to the impregnating solution inan amount up to about 2 weight percent of the total aqueous impregnatingsolution.

The amount of platinum incorporated or impregnated into thetin-containing composition should provide a concentration effective toassure predetermined butene conversion yields employing the catalystcomposition in the selective dehydrogenation of feedstock that containsn-butane. Generally, the weight percent of platinum present in theimpregnated alumina is in a range of about 0.001 to about 10 weightpercent of the impregnated zeolite composition. The preferredconcentration of platinum in the impregnated zeolite is in the range ofabout 0.01 to about 5 weight percent and, more preferably, from about0.1 to about 2 weight percent of the impregnated zeolite composition.

The platinum-impregnated tin-containing catalyst composition is treatedat an elevated temperature in the presence of an oxygen containingatmosphere, preferably air. Generally, this calcination can be conductedat a pressure in a range from below atmospheric pressure to about 1000pounds per square inch absolute (psia). More typically, however, thepressure range is from about atmospheric to about 100 psia. Thetemperature of this heat treatment is generally in the range of about400° C. to about 800° C. Preferably, this temperature range is fromabout 450° C. to about 700° C. and, most preferably, the temperature ofthis heat treatment is in a range of about 500° C. to about 600° C.

The chlorination of the calcined tin-aluminate containing platinum canbe carried out by heating with a gas containing hydrogen an at least onechlorine-containing compound which can be HCl, a chloroalkane or mixtureof these chlorination agents. Suitable chloroalkanes, which generallycontain 1-4 carbon atoms per molecule and 1-6 chlorine atoms permolecule, can be, but are not limited to, chloromethane,dichloromethane, trichloromethane, carbon tetrachloride, chloroethane,1,1-dichloroethane, 1,2-dichloroethane, trichloroethanes,tetrachloroethanes, hexachloroethanes, 1-chloropropane, 2-chloropropane,1,2-dichloropropane, 1,3-dichloropropane, 2,2-dichloropropane,trichloropropanes, tetrachloropropanes, chlorobutanes, dichlorobutanes,trichlorobutanes, tetrachlorobutanes, and the like, and mixturesthereof. HCl is the preferred chlorination agent for this invention.

The molar ratio of hydrogen to the chlorinating agent is generally about0.01:1 to about 100:1, preferably from about 0.05:1 to about 50:1, andmore preferably from about 0.2:1 to about 20:1. It is also within thescope of this invention to have an inert diluent such as nitrogen,helium, neon or argon present in the chlorination gas mixture.

The chlorination is carried out at a temperature in the range of about50° C. to about 700° C., preferably from about 150° C. to about 600° C.,more preferably from about 300° C. to about 500° C. After the materialis chlorinated it is cooled to room temperature, preferably in an inertatmosphere.

The processes of this invention applies most specifically to theconversion of n-butane to butenes and BTX. The feedstock can be anyfeedstock that contains n-butane. The higher the content of n-butane themore preferred is a feedstock for this invention. Among the feedstocksfor which this invention is useful are those having a content of crackedhydrocarbon feedstocks from the catalytic cracking e.g. fluidizedcatalytic cracking and hydrocracking) of gas oils and the thermalcracking of light hydrocarbons, naphthas, gas oils, reformates andstraight-run gasoline. The cracked gasoline feedstock generallycomprises hydrocarbons containing 2-16 carbon atoms per molecule chosenfrom among paraffins (alkanes) and/or olefins (alkenes) and/ornaphthenes (cycloalkanes). A more preferred feedstock for the process ofthis invention is a cracked gasoline derived from the fluidizedcatalytic cracking of gas oil, suitable for use as at least a gasolineblend stock generally having a boiling range of from about 80° F. toabout 430° F. The boiling range of the cracked hydrocarbon feedstock isdetermined by the standard ASTM method for measuring the initial boilingpoint and the end-point temperatures. Generally the content of paraffinsexceeds the combined content of olefins, naphthenes, and aromatics (ifpresent).

Feedstock containing n-butane and the catalyst compositions can becontacted within a reaction zone in any suitable manner. The contactingcan be operated with a catalyst bed in a reactor vessel as a batchprocess or, preferably, as a continuous process. In either a batch or acontinuous process a solid catalyst bed can be employed. Both the batchand continuous modes of operation have known advantages anddisadvantages so that one skilled in the art can select the mode mostsuitable for a particular feedstock to be contacted with the inventivecatalyst arrangement.

Contacting the feedstock containing n-butane and the catalystcomposition is carried out in a reaction zone containing the catalystcompositions while employing reaction conditions that promote theconversion of n-butane with the formation of butenes and, with thechlorinated catalyst, the formation of BTX. The reaction temperatureemployed in the contacting is in the range of from about 300° C. toabout 800° C., preferably, from about 400° C. to about 700° C. and, morepreferably, from 500° C. to about 600° C. The pressure employed in thecontacting can range from subatmospheric up to about 500 psia and,preferably, from about atmospheric to about 400 psia.

The flow rate at which the feedstock is charged to the conversionreaction zone for contact with the catalyst composition is selected toprovide a weight hourly space velocity (WHSV) in a range having anupward limit of about 1000 hour⁻¹. The term “weight hourly spacevelocity”, as used herein, shall mean the numerical ratio of the rate atwhich a cracked hydrocarbon feedstock is charged to the conversionreaction zone in pounds per hour divided by the pounds of catalystcontained in the conversion reaction zone to which the hydrocarbon ischarged. The preferred WHSV of the feed to the conversion reaction zone,or contacting zone, can be in the range of from about 0.25 hour⁻¹ toabout 250 hour⁻¹ and, more preferably, from about 0.5 hour⁻¹ to about100 hour⁻¹.

The following examples are presented to further illustrate thisinvention and are not to be construed as unduly limiting its scope.

EXAMPLE I

This example illustrates the preparation of catalysts which weresubsequently tested as catalysts in the conversion of n-butane tobutenes.

Catalyst A: Co-Impregnation of Alumina Support with Platinum and Tin

A 37 percent solution of HCl in water was added to a mixture ofchloroplatinic acid and hydrated tin chloride (SnCl₂.2H₂O) to form asolution having 1 wt percent of chloroplatinic acid, 0.65 wt percent oftin chloride, 8.35 wt percent HCl and 90 wt percent water.

A quantity of 15.27 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 9.29 g of thesolution produced above. The admixture was treated at 538° C. with airflow for 6 hours to provide 14.46 g of platinum-incorporated tinaluminate catalyst having a content of 0.244 wt percent platinum and0.220 wt percent tin.

Catalyst B: Co-Impregnation of Alumina Support with Platinum and Tin

A 37 percent solution of HCl in water was added to a mixture ofchloroplatinic acid and hydrated tin chloride (SnCl₂.2H₂O) to form asolution having 1 wt percent of chloroplatinic acid, 0.65 wt percent oftin chloride, 8.35 wt percent HCl and 90 wt percent water.

A quantity of 9.37 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 6.38 g of thesolution produced above. The admixture was treated at 538° C. with airflow for 6 hours to provide 8.80 g of platinum-incorporated tinaluminate catalyst having, a content of 0.276 wt percent platinum and0.191 wt percent tin.

Catalyst C. Co-Impregnation of Alumina Support with Platinum and Tin

A 37 percent solution of HCl in water was added to a mixture ofchloroplatinic acid and hydrated tin chloride (SnCl₂.2H₂O) to form asolution having 1 wt percent of chloroplatinic acid, 0.65 wt percent oftin chloride, 8.35 wt percent HCl and 90 wt percent water.

A quantity of 10.00 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 7.82 g of thesolution produced above. The admixture was treated at 538° C. with airflow for 6 hours to provide 9.54 g of platinum-incorporated tinaluminate catalyst having a content of 0.311 wt percent platinum and0.280 wt percent tin.

Catalyst D: Impregnation of Alumina Support with Platinum

A quantity of 10.00 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 6.57 g of a solutioncontaining 1 percent chloroplatinic acid, 1 percent HCl and 98 percentH₂O. The admixture was treated at 538° C. with air flow for 6 hours toprovide 9.47 g of platinum-incorporated aluminate catalyst having acontent of 0.264 wt percent platinum.

Catalyst E: Sequential Impregnation of Alumina Support with Tin andPlatinum

A quantity of 10.00 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 5.20 g of a solutioncontaining 1 wt percent tributyltin (Bu₃SnOAc) in C₄₋₆ solution. Themixture was treated with steam at 650° C. for 6 hours to provide 9.46 gof tin aluminate. A quantity of 10 g of the tin aluminate was admixedwith 6.93 g of a solution containing 1 percent chloroplatinic acid, 1percent HCl and 98 percent H₂O. The admixture was treated at 538° C.with air flow for 6 hours to provide 9.39 g of platinum-incorporatedtin-aluminate catalyst having a content of 0.280 wt percent platinum and0.187 wt percent tin.

Catalyst F. Sequential Impregnation of Alumina Support with Tin andPlatinum

A quantity of 10.00 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 5.37 g of a solutioncontaining 1.5 wt percent tributyltin (Bu₃SnOAc) in C₄₋₆ solution. Themixture was treated with steam at 650° C. for 6 hours to provide 9.46 gof tin aluminate. The tin aluminate was admixed with 6.81 g of asolution containing 1 percent chloroplatinic acid, 1 percent HCl and 98percent H₂O. The admixture was treated at 538° C. with air flow for 6hours to provide 9.32 g of platinum-incorporated tin-aluminate catalysthaving a content of 0.278 wt percent platinum and 0.290 wt percent tin.

Catalyst G: Sequential Impregnation of Alumina Support with Tin andPlatinum

A quantity of 10.00 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 4.91 g of a solutioncontaining 3.0 wt percent tributyltin (Bu₃SnOAc) in C₄₋₆ solution. Themixture was treated with steam at 650° C. for 6 hours to provide 9.48 gof tin aluminate. The tin aluminate was admixed with 7.20 g of asolution containing 1 percent chloroplatinic acid, 1 percent HCl and 98percent H₂O. The admixture was treated at 538° C. with air flow for 6hours to provide 9.44 g of platinum-incorporated tin-aluminate catalysthaving a content of 0.290 wt percent platinum and 0.528 wt percent tin.

Catalyst H: Sequential Impregnation of Alumina Support with Tin andPlatinum

A quantity of 10.00 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 5.20 g of a solutioncontaining 1.5 wt percent tributyltin (Bu₃SnOAc) in C₄₋₆ solution. Themixture was treated with air at 538° C. for 6 hours to provide 9.39 g oftin aluminate. The tin aluminate was admixed with 6.88 g of a solutioncontaining 1 percent chloroplatinic acid, 1 percent HCl and 98 percentH₂O. The admixture was treated at 538° C. with air flow for 6 hours toprovide 9.42 g of platinum-incorporated tin-aluminate catalyst having acontent of 0.278 wt percent platinum and 0.282 wt percent tin.

EXAMPLE II

This example illustrates the use of the Zeolite materials described inExample I as catalysts in the conversion of n-butane to butenes.

For each of the test runs, a sample of about 2.8 g of the catalystmaterials described in Example I was placed into a stainless steel tubereactor (length: about 18 inches; inner diameter: about 0.5 inch). Ann-butane feedstock was passed through the reactor at a flow rate ofabout 5 WHSV, at a temperature of about 550° C. and at atmosphericpressure (about 0 psig). Hydrogen, at a rate of 1.2 L/hr and a mol ratioof hydrogen to hydrocarbon of about 2.2, was used a carrier gas for allcatalysts. The formed reaction product exited the reactor tube andpassed through several ice-cooled traps. The liquid portion remained inthese traps and was weighed. The volume of the gaseous portion whichexited the traps was measured in a “wet test meter”. Liquid and gaseousproduct samples (collected at hourly intervals) were analyzed by meansof a gas chromatograph. Results of the test runs for Catalysts A throughH are summarized in Table I. All test data were obtained up to about 6hours on stream.

In Table I, immediately following, is listed the weight percent ofplatinum and tin in the catalysts tested. The tin and platinum areincorporated into the catalyst either by co-impregnation, impregnationor sequentially and the thermal decomposition of the catalyst isaccomplished using air calcination or a combination of steam treatingand calcination with air. The table also shows the percent conversion ofn-butane into butenes and the selectivity toward butenes andisobutylene.

TABLE I n-Butane Conversion Catalyzed with Pt/SnAl₂Ox Pt Sn Sn & PtThermal % Conv. Wt. % Select. Select. Catalyst Wt % Wt % Incorp. Decomp.n − C₄ C₄₌ C₄ ⁼ I − C₄ ⁼ A 0.244 0.220 Co-imp AC 34.507 19.565 0.5670.354 B 0.276 0.191 Co-imp AC 65.915 12.595 0.191 0.335 C 0.311 0.280Co-imp AC 13.298  5.707 0.429 0.286 D 0.264 0.000 Imp AC 15.620 10.6130.679 0.284 E 0.280 0.187 Sequent. STM-AC 36.269 29.293 0.808 0.182 F0.278 0.290 Sequent. STM-AC 31.770 25.760 0.811 0.165 G 0.290 0.528Sequent. STM-AC 22.946 19.152 0.835 0.124 H 0.278 0.282 Sequent. AC-AC26.734 21.122 0.790 0.201

A comparison of the products of the n-butane conversions shows thatCatalysts E-G impregnated sequentially and treated sequentially withsteam and air provide both better activity and better selectivity towardbutene production than either the co-impregnated Catalysts A-D or thesequentially impregnated catalyst treated only by air calcination(Catalysts A-D and H). A direct comparison between the sequentialsteam/air treatment and a sequential air/air treatment can be madenoting the conversion of n-butane, butenes produced and the selectivityto butenes and isobutylene using Catalyst F as compared to usingCatalyst H. In the comparison the much higher conversion of n-butane toC₄ is an economic compensation for the slightly lower selectivity toisobutylene.

EXAMPLE III

This example illustrates the preparation of catalysts which weresubsequently tested as catalysts in the conversion of n-butane tobutenes.

Catalyst I: Impregnation of Alumina Support with Platinum

A quantity of 10 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 6.57 g of a solutioncontaining 1 percent chloroplatinic acid, 1 percent HCl and 98 percentH₂O. The admixture was treated at 538° C. with air flow for 6 hours toprovide 9.47 g of platinum-incorporated alumina catalyst having acontent of 0.264 wt percent platinum.

Catalyst J: Chlorination of Platinum Impregnated Alumina Support

A quantity of 7.01 g of Catalyst I was treated with a flow of 100 mL perminute of hydrogen and 20 mL per minute of hydrochloric acid (HCl) at atemperature of 400° C. for 1 hour to produce 6.99 g of chlorinatedplatinum impregnated alumina.

Catalyst K: Impregnation of Alumina Support with Tin and Platinum

A quantity of 10 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 5.20 g of a solutioncontaining 1.0 wt percent tributyltin (Bu₃SnOAc) in C₄₋₆ solution. Themixture was treated with air at 538° C. for 6 hours to provide 9.46 g oftin aluminate. The tin aluminate was admixed was admixed with 6.93 g ofa solution containing 1 percent chloroplatinic acid, 1 percent HCl and98 percent H₂O. The admixture was treated at 538° C. with air flow for 6hours to provide 9.39 g of platinum-incorporated tin-aluminate catalysthaving a content of 0.280 wt percent platinum and 0.187 wt percent tinwith an atomic ration of Sn/Pt=1.097.

Catalyst L: Chlorination of Platinum Impregnated Tin-aluminate

A quantity of 6.58 g of Catalyst K was treated with a flow of 100 mL perminute of hydrogen and 20 mL per minute of hydrochloric acid (HCl) at atemperature of 400° C. for 1 hour to produce 6.62 g of chlorinatedplatinum impregnated tin-aluminate.

Catalyst M: Impregnation of Alumina Support with Tin and Platinum

A quantity of 10 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 5.37 g of a solutioncontaining 1.5 wt percent tributyltin (Bu₃SnOAc) in C₄₋₆ solution. Afterthe temperature was raised to the treatment temperature over a period of2 hours the mixture was treated with steam at 650° C. for 6 hours toprovide 9.46 g of tin aluminate. The tin aluminate was admixed with 6.81g of a solution containing 1 percent chloroplatinic acid, 1 percent HCland 98 percent H₂O. The admixture was treated at 538° C. with air flowfor 6 hours to provide 9.32 g of platinum-incorporated tin-aluminatecatalyst having a content of 0.278 wt percent platinum and 0.290 wtpercent tin with an atomic ratio of Sn/Pt=1.713.

Catalyst N: Chlorination of Platinum Impregnated Tin-aluminate

A quantity of 6.60 g of Catalyst M was treated with a flow of 100 mL perminute of hydrogen and 20 mL per minute of hydrochloric acid (HCl) at atemperature of 400° C. for 1 hour to produce 6.65 g of chlorinatedplatinum impregnated tin-aluminate.

Catalyst P: Impregnation of Alumina Support with Tin and Platinum

A quantity of 10 g of CS-331 alumina, obtained from UCI (UnitedCatalysts, Inc., Louisville, Ky.), was admixed with 4.91 g of a solutioncontaining 3.0 wt percent tributyltin (Bu₃SnOAc) in C₄₋₆ solution. Themixture was treated with air at 538° C. for 6 hours to provide 9.48 g oftin aluminate. The tin aluminate was admixed with 6.48 g of a solutioncontaining 1 percent chloroplatinic acid, 1 percent HCl and 98 percentH₂O. The admixture was treated at 538° C. with air flow for 6 hours toprovide 9.44 g of platinum-incorporated tin-aluminate catalyst having acontent of 0.290 wt percent platinum and 0.528 wt percent tin with anatomic ration of Sn/Pt=2.991.

Catalyst Q: Chlorination of Platinum Impregnated Tin-aluminate

A quantity of 6.55 g of Catalyst P was treated with a flow of 100 mL perminute of hydrogen and 20 mL per minute of hydrochloric acid (HCl) at atemperature of 400° C. for 1 hour to produce 6.57 g of chlorinatedplatinum impregnated tin-aluminate.

EXAMPLE IV

This example illustrates the use of the catalyst materials described inExample III as catalysts in the conversion of n-butane tobenzene-toluene-xylene (BTX) and C₄, particularly isobutylenes.

For each of the test runs, a sample of from about 2.5 to 2.9 g of thecatalyst materials described in Example III was placed into a stainlesssteel tube reactor (length: about 18 inches; inner diameter: about 0.5inch). The temperature was raised 10° C./min to the reaction temperatureof 500° C. while the catalyst was pretreated with a flow of 300mL/minute of hydrogen. An n-butane feedstock was passed through thereactor at a flow rate of about 5 WHSV, at a temperature of about 550°C. and at atmospheric pressure (about 0 psig). Hydrogen, at a rate of1.2 L/hr and a mol ratio of hydrogen to hydrocarbon of about 2.2, wasused a carrier gas for all catalysts. The formed reaction product exitedthe reactor tube and passed through several ice-cooled traps. The liquidportion remained in these traps and was weighed. The volume of thegaseous portion which exited the traps was measured in a “wet testmeter”. Liquid and gaseous product samples (collected at hourlyintervals) were analyzed by means of a gas chromatograph. Results of thetest runs for Catalysts A through H are summarized in Table I. All testdata were obtained up to about 6 hours on stream.

In Table II, immediately following, illustrating the conversion ofn-butane using a chlorinated platinum impregnated tin-aluminate islisted the weight percent of platinum and tin in the catalysts tested.The table also shows the percent conversion of n-butane into BTX(benzene-toluene-xylene) and butenes and the selectivity towardisobutylene.

TABLE II n-Butane Conversion Catalyzed with [Cl]Pt/SnAl₂Ox n − C₄ Wt %Comp. At. Ratio Wt % Wt % Formed Select. Catalyst Pt Sn Sn/Pt Conv. BTXC₄ ⁼s i − C₄ ⁼ I 0.264 0.000 0.000 15.620 1.322 10.613 0.284 J 0.2640.000 0.000 50.575 35.127 7.970 0.351 K 0.280 0.187 1.097 34.205 2.28228.203 0.173 L 0.280 0.187 1.097 53.613 21.037 24.516 0.325 M 0.2780.290 1.713 31.770 2.645 25.762 0.165 N 0.278 0.290 1.713 71.067 46.87116.011 0.313 P 0.290 0.528 2.991 20.994 0.000 17.404 0.118 Q 0.290 0.5282.991 75.058 53.367 13.375 0.315

The data above illustrate the superiority of the chlorinated catalystsas compared to the same catalyst without chlorination in the productionof BTX and in their selectivity toward isobutylenes.

Reasonable variations, modifications and adaptations can be made withinthe scope of the disclosure and the appended claims without departingfrom the scope of this invention.

What is claimed is:
 1. A method for the dehydrogenation of n-butane tobutenes comprising contacting a feedstock containing n-butane underreaction conditions suitable for the conversion of n-butane to butenesin the presence of a catalyst composition prepared according to themethod comprising: (A) impregnating alumina with a tin compound toprovide alumina impregnated with tin; (B) subsequently steam treatingthe alumina impregnated with tin at an elevated temperature to provide asteam treated tin-aluminate; (C) impregnating the steam treatedtin-aluminate with a platinum compound to provide a platinum containingtin-aluminate and (D) treating the platinum impregnated tin-aluminate inair at a calcining temperature to provide a calcined platinum containingtin-aluminate.
 2. A method for the dehydrogenation of n-butane tobutenes, according to claim 1 wherein the alumina is gamma alumina.
 3. Amethod for the dehydrogenation of n-butane to butenes according to claim2 wherein the tin compound is chosen from the group consisting oftributyl tin acetate, trimethyltin, tetra-n-propyltin, tributyl tinhydride, trimethyl tin hydroxide, tri-n-propyltin hydroxide,tri-n-propyltin acetate, and mixtures of two or more thereof.
 4. Amethod for the dehydrogenation of n-butane to butenes according to claim3 wherein the weight percent of tin present in the impregnated aluminais in a range of about 0.001 to about 10 weight percent of theimpregnated alumina composition.
 5. A method for the dehydrogenation ofn-butane to butenes according to claim 4 wherein the tin compound istributyl tin acetate.
 6. A method for the dehydrogenation of n-butane tobutenes according to claim 4 wherein the steam treatment is in atemperature range of about 400° C. to about 1000° C.
 7. A method for thedehydrogenation of n-butane to butenes according to claim 5 wherein thesteam treatment is in a temperature range of about 400° C. to about1000° C.
 8. A method for the dehydrogenation of n-butane to butenesaccording to claim 6 wherein the platinum compound is chosen from thegroup consisting of chloroplatinic acid, platinic chloride, platinumbromide, platinum iodide, tetramine platinum chloride, tetramineplatinum nitrate, tetramine platinum hydroxide, tetrachlorodiamineplatinum and combinations of any two or more thereof.
 9. A method forthe dehydrogenation of n-butane to butenes according to claim 7 whereinthe platinum compound is chosen from the group consisting ofchloroplatinic acid, platinic chloride, platinum bromide, platinumiodide, tetramine platinum chloride, tetramine platinum nitrate,tetramine platinum hydroxide, tetrachlorodiamine platinum andcombinations of any two or more thereof.
 10. A method for thedehydrogenation of n-butane to butenes according to claim 1 wherein thecalcining treatment is in a temperature range of about 400° C. to about800° C.